This invention relates to a unique placement for the connection between an unloader line valve and a lower pressure refrigerant line.
One of the compressor types that are especially suited for this invention is a scroll compressor. Scroll compressors are becoming widely utilized in compression applications. However, scroll compressors present several design challenges. One particular design challenge is achieving reduced capacity levels when full capacity operation is not desired.
Thus, scroll compressors, as an example, have been provided with unloader by-pass valves that divert a portion of the compressed refrigerant back to a compressor suction port. In this way, the amount of refrigerant compressed by a compressor is reduced. Of course, other compressor types may also have a by-pass valve for similar purpose, as for example, a screw compressor, where a by-pass valve can by-pass a part of refrigerant from the intermediate compression pocket within the screw compressor back to a suction line.
In a system disclosed in U.S. Pat. No. 5,996,364, a refrigerant system has both a by-pass line and an economizer circuit. The by-pass line communicates the vapor from the economizer line directly to the suction line. This by-pass line is provided with the unloader valve. When it is desired to have unloaded operation, the unloader valve is opened, and the economizer valve is closed. Refrigerant may thus then be returned from an intermediate point in the compression process directly back to suction.
U.S. Pat. No. 6,883,341 discloses an improvement to the above-described system wherein the economizer line communicates back to the main low pressure refrigerant line, not between the evaporator and the compressor, but upstream of the evaporator. Various benefits are achieved by this placement. This is disclosed in U.S. Pat. No. 6,883,341, owned by the assignee of the current application, and invented by the inventor of the current application. However, this application is limited to the situation wherein an economizer cycle is also incorporated into the system. It is also limited to a situation where only a single by-pass valve is present in the system. The present invention is directed to a compressor wherein an unloader line is not associated with an economizer cycle. The present invention also discloses an operation where several unloader lines can be present. In addition to the by-pass line being either fully open or fully closed for a prolonged period of time, the present invention also discloses a by-pass valve that can operate in a pulse width modulation regime: rapidly opening and closing to control the amount of refrigerant by-passed into the location upstream of the evaporator. The percentage of time that the valve is open determines the degree of by-pass modulation being achieved. The cycling rate of the pulse width modulated valve is selected to be shorter than the response time of the system. In this case the system does not respond fast enough to changes in the refrigerant flow through the unloader line, creating a situation where the systems responds as if the valve(s) are partially opened rather than being cycled between their open and closed positions.
While this prior art system has achieved many benefits, there are certain additional refinements that would be beneficial.